GEOG 3515

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GEOG 3515

• The Geography of South America

Class 6 Ecosystems of the Region
Music Map
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Natural Regions of South America

• As presented in Clawson (2003), there are nine
  broad macro-ecological regions in South America,
  although each will have their internal
  variations.
• They are Tropical rainforest, Tropical savanna,
  Temperate savanna, Humid subtropical,
  Meditteranean, Marine west coast rainforest,
  Highland tundra, Steppe, Desert.
• The key for classifying these regions is that the
  areas within their boundaries are more alike than
  they are different, sharing a common climate and
  associated vegetation and soil types.
• Each exhibits a different assemblage of flora and
  fauna, although some may be common to more than
  one region, and each has different economic
  potential.

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Viewing South American Ecology

• Fig 4.1 in Clawson maps out the main ecological
  regions and the combined role of climate and
  landform is discernable if one mentally
  superimposes the climate choropleths with those
  of the physiography (try it and see).
• Another way to examine the pattern of ecosystems
  and biodiversity across South America is to go to
  the United Nations Environment Programs global
  data base and play with the interactive map
  viewer zoomed in on the region.
• It can be found at http//stort.unep-wcmc.org/imap
  s/gb2002/book/viewer.htm

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Tropical Rain Forest

• Believed by biologists to generally be, hectare
  for hectare, the most biodiverse terrestrial
  region (see box 4.1).
• This region occupies the most territory, covering
  a large portion of interior Brazil, Bolivia,
  Peru, Ecuador and Colombia, and parts of the
  northern West and East coasts and the central
  East coast.
• The tropical rainforest is drought free with
  soils formed under permanent heat and wetness,
  with high and low temperatures separated by only
  a few degrees.
• Diurnal variations are greater than seasonal
  variations in temperature and much of the
  macro-fauna and insect life is active at night.
• Daytime heating and convection of moist air leads
  to afternoon thunderstorms and daily sunshine
  hours are relatively consistent year-round
  plant growth is intense.
• Temperatures may average 25-27C all year round,
  and rainfall can be 200 to 600 or more cm.

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Canopy layers

• With such abundant growth, tropical plants are
  subject to competition for light and have evolved
  to create a characteristic layering.
• The top layer is made of the forest giants that
  extends up and out as isolated crowns into the
  sunlight (40-50m).
• Below those occurs the sub-canopy at around
  20-25m and then the shrub layer at 9-12m .
• The forest floor has its own flora of mosses,
  ferns and vines that can survive in highly shaded
  and filtered, low light conditions less than 1
  gets through.
• Most macro-fauna live and feed in the trees.

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Rainforest soils

• Rainforests, when cleared for farming, can
  usually only support a few years of crop growth
  before soils become exhausted, useless and prone
  to erosion.
• Nutrient cycling, in the heat and humidity, is
  very rapid and the ecosystem functions only
  because annual accumulation of leaf and other
  organic matter on the forest floor is quickly
  decayed and reused to continue the growth of
  existing and emerging plants.

• The tropical rainforest is thus extremely
  fragile, in a delicate balance - when cleared by
  felling and burning, the ash enriched lateritic
  oxisol and ultisol soils soon become barren.
• Farmed plots are abandoned, replaced by extensive
  livestock grazing for low-grade meat production.

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Savanna

• Savanna is a term that applies to a region that
  has wet summers and dry winters (unlike our own
  Meditteranean region which is the reverse) the
  distinguising characteristic is extremes of
  precipitation.
• Savanna can either be relatively warm all year
  round (tropical) or cool (temperate) and can be
  upland or lowland in elevation.
• Savanna, especially tropical, is extensive,
  especially in the Guiana and Brazilian highlands.
• The temperate savanna occurs in a similar
  latitudinal, but at the higher altitudes of the
  Andes from Colombia through to Bolivia, where the
  cooling effect of altitude changes the
  temperature regimen to cold winters rather than
  year-round warmth.

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Savanna vegetation

• The classic savanna vegetation, for example that
  of Africa, is made up of vast expanses of tall
  grasses broken by the occasional drought-tolerant
  tree and shrub, except along water courses where
  lush, dense riparian forests occur.
• These do occur in South America but are not the
  natural climax vegetation, rather are a product
  of burning and grazing that inhibits tree
  succession.

• South American savannas naturally contain more
  deciduous trees that drop their leaves in the
  winter dry season thin and scrubby in the hot
  tropics and relatively more dense in the
  temperate higher lands.

• What can be done with the savanna is a function
  of soil oxisols are relatively useless, clay
  vertisols are favorable for ranching, and fertile
  volcanic ash/alluvium support highly productive
  farming, year-round with irrigation.

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Desert

• South Americas two big deserts are long and
  thin, one caused by the drying effect of winds
  blowing over the continent (interior desert
  Bolivia into Patagonia), the other caused by the
  dryness of the coastal air and lack of onshore
  winds as a result of cold ocean currents (coastal
  desert Peru and Chile).
• A small desert area occurs in Venezuela where
  insufficient elevation fails to strip the
  moisture from air rising out of the Caribbean
  basin.
• The coastal Atacama desert is the driest in the
  world and in some locations it will not rain for
  years on end, although a thick coastal fog called
  the garúa occurs (remember that I said it is
  captured through condensation as a water supply).

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Desert opportunities

• Natural vegetation in the South American deserts
  are, of course, limited by water availability and
  have evolved to be xerophytic, adapted to
  drought.
• Soil fertility is usually not limiting, in fact,
  surprisingly, dryland aridisols are some of the
  most fertile in the world if water can be brought
  in.
• With high potential evapotranspiration, however,
  irrigation can result in mobilization and
  concentration of salts and the salinization of
  the all important topsoil layer, inhibiting plant
  growth.

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Steppe

• The semi-arid transition between the arid and the
  humid zones is called steppe and South America
  has two long steppes on either side of its
  interior desert and an area of semi-arid steppe
  contained within a humid zone up on the Brazilian
  plateau, associated with inter-tropical
  convergence and lulls in coastal air mass
  movement.
• Steppes are also called prairies and are
  generally drier than the savanna, having shorter
  grasses.
• South American steppes generally have more trees
  than their North American or Eurasian
  counterparts, often thorny and scrubby, and are
  known locally by different names such as monte,
  caatinga, and are burned to stimulate grass
  takeover.
• Extensive cattle grazing has been the main use of
  the Steppes, although since soils are good,
  agriculture is possible with irrigation.
• South American steppes have been invaded by
  exotic, introduced grass species, mostly from
  Africa.

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Burning as a Land Management Tool
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Humid Subtropical

• The most important food producing and highly
  settled region owing to its mild temperatures and
  its almost year-round precipitation averaging at
  100 or more inches.
• Organic material, in some cases augmented by
  volcanic minerals, has built up to create deep,
  fertile soils such as the molisols of the Pampa.
• Covers a broad section of Argentina, Uruguay and
  Brazil the Pampa and the Paraná Plateau.
• Most of the original vegetation mixed
  grasslands and lowland broadleaf and upland
  conifer forests - as with northern Europe, has
  been long replaced with grass and crops.
• Most of the conversion was done by European
  settlers in the 1800-1900s, who reproduced what
  they had done back home.

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Mediterranean

• The Mediterranean climate is our very own Bay
  Area climate mild temperatures with a hot and
  dry summer and a cool and wet winter in which
  almost all the rain will fall in a five month
  period.
• In South America, this is wholly contained in a
  smallish area of Chile, which has the same type
  of Chaparral natural vegetation and excellent
  alfisol soils that we have.
• As with our Sierra snowmelt, Chiles
  Mediterranean region has Andean runoff which can
  be used for irrigation, resulting in extensive
  agricultural production geared to export,
  particularly to the winter markets of North
  America.

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Marine West Coast Rain Forest

• As with the Pacific Northwest (only upside down),
  South America has its marine west coast rain
  forest to the south of its Mediterranean region
  with year-round cooler weather.
• The seemingly mild temperatures are reduced for
  humans and animals by the wind-chill factors due
  to the roaring, Antarctic pressure belt induced
  onshore winds that are the southern hemisphere
  westerlies.
• Rainfall is high, often well over 200 inches a
  year and conditions are Seattle-like permanently
  overcast and cloudy.
• Mixed forests predominate with dense, low
  understories of ferns, grasses, mosses and vines
  tolerant of leached, acidic soils low in nutrient
  content.
• Agricultural potential, other than forestry and
  sheep, is limited except in the transitional zone
  close to the Mediterranean zones good for
  orchards, grains and dairy.

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The Highlands

• Very hard to characterize on a map because of the
  altitudinal effects that creates interspersed
  patches and strips of land that have markedly
  different temperature regimens.
• Remarkable (see Table 4.8) is the incredible
  consistency in average monthly temperature over
  the year, regardless of whether a location is in
  tierra caliente, templada, fría or helada.
• Depending on if wet or dry and the seasonality,
  the caliente, templada and fría will resemble
  the different regional types previously
  presented.
• The helada is the only truly unique environment
  in this grouping of highlands, occupying all the
  high peaks, even up into the tropical zones of
  Ecuador and Colombia, and broad interconnected
  ridge and high plateau areas from Central Chile
  through Bolivia and Peru.

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Tierra Helada

• A highly erosional environment with mechanical
  glacial and peri-glacial (freeze-thaw) activity
  but limited chemical decomposition.
• Soils are thus thin and poorly developed,
  supporting herbaceous plants typical of the
  arctic tundra or rocky mountain high meadows
  bunch grasses being principal.
• In the drier areas, the vegetation is called puna
  and is grasses and herbs and where wetter, it is
  called párana and includes mosses and shrubs.
• Lower altitudes with frost-free growing seasons
  are extensively cultivated for vegetables, tubors
  and so forth and the less conducive altitudes are
  used for cattle and for llamas, vicunas and
  alpacas.

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The Status of South American Bioregions

• An extensive report on the biodiversity of South
  America, published in 1996 by the IUCN/UICN,
  highlighted the ecological spectrum of South
  America and the challenges of conservation.
• With a total area of 1,753m hectares, in 1996
  some 870m (50) were forested, 69 of the
  original natural forest cover of the region pre
  human exploitation.
• Some 610m hectares (35) were devoted to crops
  (115m) or grazing (495m), and only 7.4 of the
  total land mass was classified as being a
  protected area in a national park or other such
  reserve.
• Rates of deforestation are intense in many areas,
  removing as much as 5 of the remaining stock per
  year.

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Exploring South American Nature

• Although a great deal of the South American
  ecosystems have not been explored in great
  detail, most of the macro fauna and flora are
  well documented and researched.
• From the early discovery and classification of
  plants and animals by the Spanish colonizers,
  through the work of the botanic prospectors of
  the multinational fruit companies, to the work of
  biological researchers from across the globe, a
  wealth of information exists.
• One of the most comprehensive databases for Latin
  America, including the South American nations, is
  at Infonatura - http//www.natureserve.org/infonat
  ura/servlet/InfoNatura
• For any species, with either a common or
  scientifica name, it is possible to access a
  database of information, maps of distribution,
  and published literature check it out.
• Sectional surveys suggest that many thousands of
  insects and arachnids remain to be discovered and
  a lesser number of plants.